Heterostructure Cu₂O@TiO₂Nanotube Array Coated Titanium Anode for Efficient Photoelectrocatalytic Oxidation of As(III) in Aqueous Solution

Addressing the ever-growing arsenite pollution in groundwater has become an essential and urgent issue for ensuring the safety of human beings and the environment. It is highly attractive to preoxidize As(III) to relatively low toxic As(V) for further efficient arsenic removal by adsorption, ion exchange, or coagulation. In this study, a novel heterostructure Cu₂O@TiO₂nanotube array coated titanium anode (CTNTA) was fabricated by combination of electrochemical anodization and electrodeposition and used for the highly efficient photoelectrocatalytic oxidation conversion of As(III) to As(V) in aqueous solution. The morphology, composition, and photoelectric performances of the CTNTA anode were systematically characterized. The effect of the loading amount of Cu₂O nanoparticles on the photoelectrocatalytic oxidation kinetics of As(III) was investigated, and the comparison study among photocatalytic, electrocatalytic, and photoelectrocatalytic oxidations of As(III) was also explored to demonstrate the synergistic effect of As(III) oxidation conversion performance. The heterostructure CTNTAs-1.00 delivered a substantially enhanced photoelectrocatalytic oxidation ratio of As(III) at 95% within 30 min at a current density of 10 mA·cm^-2under visible-light irradiation. The electrochemical deposition amount of Cu₂O nanoparticles on TiO₂nanotube arrays (TNTAs) was found to be positively correlated with the achievement of boosted As(III) oxidation efficiency. The high photoelectrocatalytic oxidation performance of the CTNTA was ascribed to the favored separation efficiency of photoinduced carriers and electron-hole pairs under both visible light irradiation and electric potential conditions. The photoelectrocatalytic oxidation reaction mechanism was proven to be ascribed to the active species of holes (h⁺), superoxide radicals (^•O₂^-), and hydroxyl radicals (^•OH). These results highlight the high conversion rate of As(III) by the photoelectrocatalytic oxidation reaction on such a nanostructured anode, which offers a promising methodology for further in-depth oxidation of As(III) in aqueous solution.